Iranian short-range Nasr missile is launched during navy war games near the Strait of Hormuz in southern Iran. (Ebrahim Noroozi/AFP/Getty Images)

The Obama Administration brushed aside Iran's warning to keep U.S. aircraft carriers out of the Gulf, dismissing its threats as a consequence of hard-hitting American sanctions on the Iranian economy.

Provoking a hostile start to what could prove a pivotal year for Iran, the country's army chief said American vessels were unwelcome in the Gulf, the strategic waterway that carries to market much of the oil pumped in the Middle East.

The Islamic republic also has warned of blocking one of the world's key tanker lanes, the Strait of Hormuz, in response to new, stronger U.S. economic penalties on Iran over its disputed nuclear enrichment program.

Iranian Gen. Ataollah Salehi's warning about the Gulf came just three days after President Barack Obama signed into law new sanctions targeting Iran's Central Bank and its ability to sell petroleum abroad.

Just Iranian sabre-rattling, with no effect on U.S. plans or military movements, spokesmen in Washington said.

"It's the latest round of Iranian threats and is confirmation that Tehran is under increasing pressure for its continued failure to live up to its international obligations," White House Press Secretary Jay Carney said.

"Iran is isolated and is seeking to divert attention from its behaviour and domestic problems," Carney added.

Salehi didn't cite a specific vessel, but the U.S. Navy's 5th Fleet has said the aircraft carrier USS John C. Stennis and another vessel headed out from the Gulf and through the Strait of Hormuz last week after a visit to Dubai's Jebel Ali port.

Iran closed 10 days of naval manoeuvres Tuesday, continuing a tone of military defiance but seeing the bite of international sanctions pull its currency, the rial, down to lows against the dollar earlier this week.

Pentagon spokesman George Little said the Navy operates in the Gulf in accordance with international law, maintaining "a constant state of high vigilance" to ensure the flow of sea commerce.

"The deployment of U.S. military assets in the Persian Gulf region will continue as it has for decades," Little said in a written statement.

"These are regularly scheduled movements in accordance with our longstanding commitments to the security and stability of the region and in support of ongoing operations."

Iranian nuclear ambitions

The 5th Fleet has long been headquartered in the Gulf state of Bahrain, serving as a key counterbalance to Iran's expanding military presence in the Gulf.

American allies France and Britain also have warships stationed in the region, while key Arab partners Saudi Arabia and the United Arab Emirates closed deals last week with the U.S. for major arms purchases.

The threat of a military confrontation appears to be rising.

If Iran advances closer to the production of an atomic bomb, it would increase the chances of Israel launching a pre-emptive strike on facilities to prevent what it sees as a mortal threat to its existence.

The United States and some European countries may co-operate, or choose to intervene militarily themselves.

The West fears an atomic Iran would not only destabilize Israel — Tehran's biggest enemy — but also much of the Arab world.

Iran denies it is seeking a weapon but insists on the right to enrich uranium for what it claims to be an energy program.

For now, the Obama Administration says all options are on the table.

And it is unclear how far away Tehran would be from nuclear weapons potential, despite a recent report by the UN's International Atomic Energy Agency detailing Iranian experiments whose sole purpose is the development of nuclear arms.

It was the strongest sign yet that it seeks to build a nuclear arsenal, despite Iran's claims that its enrichment activity is entirely for peaceful purposes.

On Monday, Iran test-fired a surface-to-surface cruise missile as part of its naval manoeuvres in the Gulf, prompting Iran's navy chief to boast that the strait is "completely under our control."